Assays that employ mammalian enzymes (generally mixed-function oxidases from rat liver) to provide metabolic activation of premutagens to ultimate mutagens have been developed, and are widely used to identify mutagenic compounds. It is now clear that some compounds are activated by other oxidizing enzymes, such as peroxidases, that are not present in rat liver S-9 preparations. However, the use of peroxidases in routine mutagenicity screening has been limited by the commercial unavailability of mammalian peroxidases. We propose to develop and commercialize a short-term mutagenicity assay that employs a mammalian peroxidase to provide metabolic activation and Salmonella typhimurium to detect mutagens. In Phase I, we will develop conditions to maximally activate a series of aromatic amines to mutagens by highly purified prostaglandin H synthase. The same conditions will be used in Phase II to screen a variety of structurally unrelated compounds for peroxidase-induced mutagenicity. These experiments will provide the basis for a new mutagenicity screening system based on an alternative pathway of metabolic activation.